St Martin's (Sint-Martinuskerk) is Aalst's main church, a striking but unfinished Gothic structure begun in 1480 and never completed to the planned dimensions. The choir and transept are still impressive, and the church holds a notable collection of paintings.
The standout is a Rubens altarpiece showing St Roch interceding for plague victims — one of relatively few major Rubens works in this part of Flanders.